Alobar Holoprosencephaly in an Aborted American Quarter Horse Fetus.
Authors: Henker Luan Cleber, Lorenzett Marina Paula, Piva Manoela Marchezan, Wronski Júlia Gabriela, de Andrade Danilo Giorgi Abranches, Borges Alexandre Secorun, Driemeier David, Oliveira-Filho José Paes, Pavarini Saulo Petinatti
Journal: Journal of equine veterinary science
Summary
Alobar holoprosencephaly, a severe developmental malformation involving complete failure of the prosencephalon to divide into two hemispheres, has been well-documented in human and some animal species but had not previously been reported in equines until this case study of an aborted American Quarter Horse fetus at nine months gestation. The authors performed detailed postmortem examination and genetic sequencing of the three coding exons of the sonic hedgehog (SHH) gene—a key regulator implicated in holoprosencephaly across species—using liver tissue from the affected foetus. The fetus presented with severe craniofacial defects including maxillary and nasal bone hypoplasia, bilateral absence of the eyes, and a single, nearly spherical brain lobe with complete fusion of the thalami and absence of olfactory and optic structures, yet no pathogenic polymorphisms in the SHH coding regions were identified. These findings suggest that whilst SHH mutations may not underlie this particular case, other genetic or environmental factors during critical developmental windows warrant investigation in equine holoprosencephaly. Veterinary practitioners should be aware of this condition as a differential diagnosis in cases of severe congenital facial deformity and early fetal loss, particularly given the Quarter Horse involvement, though the genetic aetiology remains to be fully elucidated.
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Practical Takeaways
- •Breeders of American Quarter Horses should be aware that holoprosencephaly, previously undocumented in horses, can cause severe fetal malformations and abortion; genetic counseling and family history review may be warranted for affected lines
- •Veterinarians performing postmortem examination on aborted equine fetuses should recognize the characteristic features of holoprosencephaly (single brain lobe, fused thalami, severe facial/skull defects) to enable proper diagnosis and genetic investigation
- •SHH gene mutations are not the only genetic cause of equine holoprosencephaly; further research into other candidate genes and non-coding regions is needed for accurate breeding recommendations
Key Findings
- •First documented case of alobar holoprosencephaly in an equine species (aborted American Quarter Horse fetus at 9 months gestation)
- •Severe phenotypic manifestations included complete absence of maxillary and nasal bones, bilateral anophthalmia, and single fused prosencephalon with monoventricle
- •Sequencing of three SHH gene coding exons revealed no polymorphisms in the coding region despite classic holoprosencephaly presentation, suggesting potential non-coding mutations or other genetic/environmental factors